feat: Update opencensus metrics to include bigtable resource ids and …

…rpc level metrics

This PR refactors opencensus metrics integration to use gax's ApiTracers.
Which allows this client to instrument individual attempts and tag everything
with bigtable resource ids

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/metrics/CompositeTracer.java

@@ -0,0 +1,154 @@
+/*
+ * Copyright 2020 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.cloud.bigtable.data.v2.stub.metrics;
+
+import com.google.api.gax.tracing.ApiTracer;
+import com.google.common.collect.ImmutableList;
+import java.util.ArrayList;
+import java.util.List;
+import org.threeten.bp.Duration;
+
+/** Combines multiple {@link ApiTracer}s into a single {@link ApiTracer}. */
+class CompositeTracer implements ApiTracer {
+  private final List<ApiTracer> children;
+
+  CompositeTracer(List<ApiTracer> children) {
+    this.children = ImmutableList.copyOf(children);
+  }
+
+  @Override
+  public Scope inScope() {
+    final List<Scope> childScopes = new ArrayList<>(children.size());
+
+    for (ApiTracer child : children) {
+      childScopes.add(child.inScope());
+    }
+
+    return new Scope() {
+      @Override
+      public void close() {
+        for (Scope childScope : childScopes) {
+          childScope.close();
+        }
+      }
+    };
+  }
+
+  @Override
+  public void operationSucceeded() {
+    for (ApiTracer child : children) {
+      child.operationSucceeded();
+    }
+  }
+
+  @Override
+  public void operationCancelled() {
+    for (ApiTracer child : children) {
+      child.operationCancelled();
+    }
+  }
+
+  @Override
+  public void operationFailed(Throwable error) {
+    for (ApiTracer child : children) {
+      child.operationFailed(error);
+    }
+  }
+
+  @Override
+  public void connectionSelected(String id) {
+    for (ApiTracer child : children) {
+      child.connectionSelected(id);
+    }
+  }
+
+  @Override
+  public void attemptStarted(int attemptNumber) {
+    for (ApiTracer child : children) {
+      child.attemptStarted(attemptNumber);
+    }
+  }
+
+  @Override
+  public void attemptSucceeded() {
+    for (ApiTracer child : children) {
+      child.attemptSucceeded();
+    }
+  }
+
+  @Override
+  public void attemptCancelled() {
+    for (ApiTracer child : children) {
+      child.attemptCancelled();
+    }
+  }
+
+  @Override
+  public void attemptFailed(Throwable error, Duration delay) {
+    for (ApiTracer child : children) {
+      child.attemptFailed(error, delay);
+    }
+  }
+
+  @Override
+  public void attemptFailedRetriesExhausted(Throwable error) {
+    for (ApiTracer child : children) {
+      child.attemptFailedRetriesExhausted(error);
+    }
+  }
+
+  @Override
+  public void attemptPermanentFailure(Throwable error) {
+    for (ApiTracer child : children) {
+      child.attemptPermanentFailure(error);
+    }
+  }
+
+  @Override
+  public void lroStartFailed(Throwable error) {
+    for (ApiTracer child : children) {
+      child.lroStartFailed(error);
+    }
+  }
+
+  @Override
+  public void lroStartSucceeded() {
+    for (ApiTracer child : children) {
+      child.lroStartSucceeded();
+    }
+  }
+
+  @Override
+  public void responseReceived() {
+    for (ApiTracer child : children) {
+      child.responseReceived();
+    }
+  }
+
+  @Override
+  public void requestSent() {
+    for (ApiTracer child : children) {
+      child.requestSent();
+    }
+  }
+
+  @Override
+  public void batchRequestSent(long elementCount, long requestSize) {
+    for (ApiTracer child : children) {
+      child.batchRequestSent(elementCount, requestSize);
+    }
+  }
+}